This invention relates to a welding repair method for a metal member and a build-up welding apparatus used for this method. This invention can be applied to make minor corrections to the size of metal member, such as metal molds for rubber or synthetic resin products, and the like, and to repair a relatively minutely flawed portion of such metal member.
Metal molds are frequently flawed or distorted in size during the manufacturing process or when later put to use. It is often economically desirable to restore such metal molds by correcting or repairing the flawed portion or the size distortion. A build-up argon welding is now common for repairing and correcting such problems. According to such welding method, a welding rod is melted by arc in an argon atmosphere, the build-up welding is carried out at a fusion zone of the metal member, any extra welded portion is worn away after solidifying, and the repair is completed by grounding. Since this build-up argon welding method requires a continuous generation of a high 6,000 through 8,000 degree centigrade arc heat to melt the welding rod, various problems relating to heat may occur such as sinking and variation in shape and color of the metal member. Therefore, the build-up argon welding may not be proper for a relatively small correction or repair.
Other correction and repair methods have been proposed, including (a) silver brazing, (b) build-up metabolizing plating, (c) beating, and (d) embedding with insert. These methods have advantages but have many kinds of disadvantages which limit the ability to correct or repair the metal molds. For example, methods (a), (b) and (c) have poor endurance. Repair methods (b) and (d) require a long operation time and the repair method (c) requires a degree of technical skill. In addition, all of the methods (a) through (d) are inappropriate for correcting fine problems.
Japanese Unexamined Patent Publication No. 5-261585 and No. 5-261556 (both corresponding to U.S. Pat. No. 5,378,867) disclose a repairing method using welding and a build-up welding apparatus which can be used to repair a relatively minute collapsing or flawed portion of a metal member or to correct the size of the metal member, such as a metal mold for forming synthetic resin. According to the cited publications, a secondary electrode is connected to the metal member and a proper volume of fine welding powder is piled onto the portion of the metal member to be repaired or, alternatively, a thin sheet-type welding material is provided thereon. The welding powder or the welding material is pressed to the metal member locally and a large pulse current of about 300-1500 amperes is applied at the conduction point for a short period of about 1/1000-4/1000 seconds to form nuggets of welding on the metal member. Thus, the melted metal is built up on the part to be repaired in the form of dots or lines or as a layer. After solidifying, the excessively padded part of the build-up welding is removed and ground or polished. This repair method using welding and the build-up welding apparatus can accomplish alloy welding forming a single body for which the welded strength (the alloying factor) of the melted metal and the endurance of the weld are both strong and it is hard to separate the welded part from the metal member.
However, a detailed observation with a magnified microscopic photograph or the like shows the build-up welded portion (welded metal) has about 95% of the welding factor or alloying factor rather than 100%. The welding factor depends on the technical level of the worker since the welded metal (nuggets) may not be welded continuously due to a slight movement error during operation with the primary electrode. This is because each nugget is formed as a fine dot of about 0.6-1 mm diameter by a single pulse from the primary electrode of the build-up welding apparatus. These dot-shaped nuggets are coupled to each other or piled up as layers for build-up welding. A poor welding factor results in a separation of the build-up welded portion and failure of the repair.
It is therefore an object of the present invention to provide a repairing and correcting method and an apparatus for build-up welding that is appropriate for minute repairs and corrections without adversely affecting the metal member with excess heat.
It is another object of the present invention to provide a repairing/correction method and a build-up welding apparatus for such method wherein the build-up portion (welded metal) has excellent durability and quality, the repair and correction operation can be performed in a short time, and a high degree of technical skill is not required.